Fluoropolymers are excellent in flame retardancy, nonstickiness and electrical insulating properties, among others, and therefore have so far been utilized as moldings or covering materials in various fields such as the chemical industry and machine industry.
In recent years, the use of tetrafluoroethylene [TFE]/hexafluoropropylene [HFP] copolymers and TFE/HFP/perfluoro(alkyl vinyl ether) copolymers as covering materials in electric wire jackets and LAN cables has been proposed; for use as electric wire coverings, however, such copolymers are required to be capable of being extrusion-molded at a high speed in electric wire covering.
Known as fluoropolymers capable of being extrusion-molded at a high speed are, for example:
TFE/HFP copolymers which are essentially composed of 78 to 95% by weight of TFE monomer units, 5 to 22% by weight of HFP monomer units and at most 3% by weight of units derived from a fluoromonomer copolymerizable with TFE and HFP, show a molecular weight distribution within a specified range, contain less than 80 unstable terminal groups per 1×106 carbon atoms and can be obtained by aqueous emulsion polymerization (cf. e.g. Patent Document 1);
Fluorocopolymers which comprise constituent units derived from TFE and HFP and at least one of specified perfluoro (alkyl vinyl ether) species in a content ratio of 75 to 92:8 to 20:0 to 5 by weight, have a melt flow rate (372° C., 5000 g load) within the range of 10 to 35 (g/10 minutes) and show a die swell within the range of 5 to 20% (cf. e.g. Patent Document 2);
Fluorocopolymers which are obtained by polymerization of TFE and HFP, if desired together with a perfluoro (vinyl ether) as a monomer, with the weight ratio among the respective monomer contents being 70 to 95:5 to 20:0 to 10, and which have a melt flow rate of 30 g (g/10 minutes) or higher, a volatile matter content of not higher than 0.2% by weight and a stress relaxation modulus within a specified range (cf. e.g. Patent Document 3);
FEP pellets with a volatile matter content not exceeding 0.2 weight % which, when used to form an insulating layer over a core wire by extrusion coating at a coating speed of 2800 ft/minute, meet the following requirements: (i) an adhesive strength between the insulating material and the core wire of 0.8 kg or more and (ii) an average number of cone-breaks in the insulating layer of one or less per 50,000 ft of the coated core wire (cf. e.g. Patent Document 4); and
Fluoropolymers which are composed of 78 to 95 mass % of TFE and 5 to 22 weight % of HFP, optionally together with up to 3 mol % of a third monomer or monomers copolymerizable with TFE and HFP, and have a ratio of weight average molecular weight to number average molecular weight of less than 2 and a melt flow index of not lower than 15 (cf. e.g. Patent Document 5).    Patent Document 1: International Publication WO 00/44797    Patent Document 2: International Publication WO 01/36504    Patent Document 3: U.S. Pat. No. 6,703,464    Patent Document 4: U.S. Pat. No. 6,743,508    Patent Document 5: U.S. Pat. No. 6,541,588